Modifying an Array Passed as an Argument to a Function in Swift

Modifying an array passed as an argument to a function in Swift

You need to change the definition of modify to accept an inout parameter. By default, function arguments are immutable, but by using the inout keyword, you can make them mutable. You also need to pass the argument by reference.

func modify( arr: inout [String]) {
    arr.removeFirst()
}
var stringArr = ["a","b"]
modify(arr: &stringArr) //stringArr = ["b"] after the function call

Swift - Changing an array value of function call

This is because f parameter is an immutable array. You can change this to a mutable array parameter by using the function signature as follows

func calculateBoundary (var f:[Float], var s:[Float], n:NSInteger)  -> (forceBound1:Float, forceBound2: Float, displacement:[Float]) { // }

If you want to also modify the original arrays passed to the function, you need to use inout parameters.

func calculateBoundary (inout f:[Float],inout s:[Float], n:NSInteger) -> (forceBound1:Float, forceBound2: Float, displacement:[Float]) { // }

You can call it like this

var f : [Float] = [1.0,2.0]
var g : [Float] = [1.0,2.0]

let result = calculateBoundary(&f, &g, 1)

How do you modify array parameter in swift

func tt(a:[UInt8]) {
    a[2]=10
}

In above function, the function parameter a is a let constant, you can't change it inside the function.

You need to use inout parameter to be able to modify this.

var a: [UInt8] = [1,2,3,4,5]
func tt(a: inout [UInt8]) {
    a[2] = 10
}
tt(a: &a)

modify an array within a function does not work

The arrays inside alter_them are a copy of the originals.

Use inout to modify the original arrays:

func alter_them(inout data: [String], inout data2: [String]){
    for (i, _) in data.enumerate(){
        data[i] = "1"
    }
    for (i, _) in data2.enumerate(){
        data2[i] = "2"
    }
}

alter_them(&Draw_S, data2: &Draw_E)

Passing an array to a function with variable number of args in Swift

Splatting is not in the language yet, as confirmed by the devs. Workaround for now is to use an overload or wait if you cannot add overloads.

How to pass an Array to function as a parameter in Swift?

You can simply use [DataModel] as type for function parameter

Something like

func parsedData(parsedResuls: [DataModel]) {

}

Swift: Pass array by reference?

Structs in Swift are passed by value, but you can use the inout modifier to modify your array (see answers below). Classes are passed by reference. Array and Dictionary in Swift are implemented as structs.

Trying to pass an array to function in swift

Every language has a natural way code wants to be written. As part of the process for learning a language, try to learn how code should be written in that language.

In this example, you want to combine the elements of two arrays into an array of dictionaries, randomly select 10 of those dictionaries. In Swift, zip(), map() and prefix() cover everything except the randomization. You need something like a shuffle method for the array.

Here is one that does the Fisher-Yates (fast and uniform) shuffle:

extension CollectionType {
    func shuffle() -> [Generator.Element] {
        var result = Array(self)

        if result.count > 1 {
            for i in 0 ..< result.count - 1 {
                let j = Int(arc4random_uniform(UInt32(result.count - i))) + i
                if i != j {
                    swap(&result[i], &result[j])
                }
            }
        }

        return result
    }
}

With shuffle() in hand, I can solve the problem.

let allQuestions = zip(iN, nS).map {xx, yy in ["x": xx, "y": yy]}
let shuffledQuestions = allQuestions.shuffle()
let first10ShuffledQuestions = shuffledQuestions.prefix(10)

let questionsArray: [AnyObject] = Array(first10ShuffledQuestions)

The first part, zip(iN, nS).map {xx, yy in ["x": xx, "y": yy]} creates an array of dictionaries using the key "x" for iN and "y" for nS. The next part, shuffle() returns an array of dictionaries in a random order. The last part, prefix(10) returns an array slice of the shuffled array containing the first 10 elements. Because prefix() returns an array slice and not an array, use Array() to create an array from the array slice for the final assignment to questionsArray.

This can all be done in one line.

let questionsArray: [AnyObject] = Array(zip(iN, nS).map {xx, yy in ["x": xx, "y": yy]}.shuffle().prefix(10))

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